Like most people my gut reaction was "that's not possible" and in fact I believe that depending on how you define "sailing dead downwind" it may or may not be p

Like most people my gut reaction was "that's not possible" and in fact I believe that depending on how you define "sailing dead downwind" it may or may not be possible. It is clear that the angle of attack of the sails is not at 90 degrees to the wind therefore strictly speaking perhaps this is not sailing dead downwind. It is well known that sail driven vehicles can greatly exceed actual wind speed due to "apparent wind" effects among others.